In today's society, the ability to quickly and efficiently store and retrieve digital information onto mass storage devices is becoming ever-more important. One such mass storage device is a hard disk drive (‘HDD’).
Typically, a magnetic head of an HDD has a Head-Disk Contact (‘HDC’) detection sensor, which detects a contact between the head and a disk media, referred to as a ‘touch-down’. Generally speaking, the Head-Disk Contact detection sensor outputs a transient signal in response to such received impulses. A transient signal which exceeds a certain level is therefore recognized as a head-disk contact. This can occur during read mode or a write mode.
However, in certain noisy conditions, for example, a ‘write’ mode, which can be wherein a preamplifier drives a ‘write’ current to record a digital signal on the HDD, a distinction between a ‘touch-down’ signal and noise is difficult. In other words, it can be difficult to determine in some noisy environments whether a ‘touch-down’ has actually occurred.
In order to address this difficulty and ambiguity, various signal processing schemes have been employed. A RMS or peak-detection applied to a received Head-Disk Contact signal can be utilized. Generally speaking, if a RMS threshold or a peak-detection threshold is exceeded, a ‘touch-down’ is deemed to have occurred. Indeed, employment of the RMS value or peak value in one or multiple rotations is good criteria to judge head-disk touch-down (See FIG. 5) due to such factors as a defect or a roughness of a disk surface of the HDD.
However, these threshold detection schemes introduce further complications into a determination of when a ‘touch-down’ has occurred. For example, one rotation of the HDD, used for RMS and peak detection is more than millisecond. This can be unacceptably long. In the case of a 5400 rpm HDD, a rotation period is 11 mS, again, a long time period. Conventional implementations of RMS and peak detection for detection over this long time period typically require a very large area.
Therefore, there is a need in the art for to RMS and peak detection in touch-down detectors that addresses at least some of the concerns of conventional touch-down detection.